Feeding ecology of the alien invasive pulmonate, Theba pisana (White garden snail), in the West Coast National Park, South Africa

Theba pisana (White Garden snail), is native to both Southern Europe and Northern Africa, and was introduced to South Africa in 1881. Since then, it has become widely distributed along the coast, including the West Coast National Park (WCNP). This study aimed to determine the feeding ecology (i.e. feeding duration & consumption rate) of T. pisana, and thus the impact on the vegetation. Field observations to determine the feeding duration was conducted by observing snails on their naturally occurring vegetation every two-hours for twenty-four-hours over varying weather conditions. Temperature (C) and humidity (%) were recorded every two hours. Laboratory experiments were performed to determine the consumption rate of five naturally occurring plant species (Euphorbia mauritanica, Chrysanthemoides incana, Willdenowia incurvata, Ruschia macowanii, Lebeckia spinescence) as well as the cultured diet (cabbage leaves). The results showed that T. pisana are inactive in high temperatures (20.4–28 C), slightly active (10%) in low temperatures (4-8C) and high humidity (85-96%), and largely active (87-96%) when a constant humidity (49-72%) or sudden moisture (e.g. rain) (56-73%) is experienced irrespective of temperature. Snails preferred cabbage leaves (0.089g/day) to the naturally occurring plant species. With approximately 4.04 snails per m2 in the park and snails being active approximately 120 days (i.e. no. of rainy days), the annual potential consumption rate would be 13.5 g/snail on a naturally occurring food item (e.g. Chrysanthemoides incana 0.028g/day). With this low density, T. pisana might not pose an immediate threat, but the eradication is still important for the continual success of the WCNP as a conservational area.